Zn-ln-O based thin-film transistors: Compositional dependence

The compositional dependence of sputter-deposited Zn-In-O (ZIO) film properties and the TFT performance were studied by means of a combinatorial technique. Both the characteristics of ZIO TFTs and the ZIO film properties are very sensitive to the Zn:In ratio. The best TFT performances are obtained at Zn:In similar to 60:40 at%, where the saturation mobility (mu(sat)), subthreshold swing (S.S.), on-off current ratio (I-on/I-off), and threshold voltage (V-th) are 26.5 cm(2)/Vs, 0.24 V/dec., 10(10), and +2 V, respectively. The TFT characteristics speak at this compositional ratio. Specifically, mu(sat), I-on/I-off and V-th reach maximum, while S.S. reaches minimum at this ratio. The air stability of ZIO-TFTs was also examined for active channel layers with different Zn:In ratios, which clarified that the TFTs with high stability are obtained around the same composition ration where the best characteristics are obtained. It was confirmed by X-ray diffraction and transmission electron microscopy that the ZIO films with this composition ratio have amorphous structure. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.